Cobalt-base alloys



United States Patent COBALT -BASE ALLOYS James F. Baldwin, New York, N.Y., and (l. Sheets, Fairlawn, N. J., assignors to CoastMetals, Inc,Little Ferry, N. J., a corporation of Delaware No Drawing. ApplicationSeptember 30, 1955, Serial No. 537,876

2 Claims. (Cl. 75-134) This invention relates generally to hightemperature alloys, but has reference more particularly to cobalt-basealloys of the Stellite type.

It has been generally known that increasing the tungsten content ofcobalt-base alloys, such as alloys of the Stellite type, resulted inincreased high temperature properties, but it was also thought that theimprovement in high temperature properties would necessarily be uniformin character.

As the result of tests which have been conducted in connection withcertain jet guided missile parts, we have discovered that theimprovement in high temperature properties, resulting from theincorporation of increasingly larger amounts of tungsten in suchcobalt-base alloys is not uniform, but that a marked and sudden increasein the improvement occurs when the tungsten reaches a value of about18.75%, and that this improvement is effective up to a value of about23.25% tungsten, beyond which there is no further improvement ofconsequence.

The aforesaid tests were conducted on lap joint test specimens made ofstainless steel, with the cobalt base alloy of the present inventionapplied as a fillet on both sides of the lap joint. Precautions weretaken to prevent any of the fillet material from flowing into the joint,and the fillets were maintained uniform as to dimensions in all of thetest specimens.

The test specimens were heated to a temperature of 1600 F., andmaintained at such temperature for 20 minutes, after which each specimenwas subjected to a test to determine its ultimate strength at thistemperature. In this way, assurance was had not only that each testpiece had arrived at the desired temperature, but also that stresseswhich might have been produced by the welding operations incidental toformation of the fillets had been substantially eliminated. The resultsof these tests may be tabulated as follows:

Ultimate Alloy Carbon Chro- Cobalt Tung- Silicon Iron Strength No. miumsten at 1,600" F., p. s. i.

In the aforesaid alloys, the balance of the alloy, in each case,consists of small and inconsequential amounts of residual or traceelements, such as manganese, sulphur, and vanadium. Vanadium is usuallyadded to obtain grain refinement in the alloy, and when thus used, maybe present in amounts up to about 2%. It improves the Patented July 30,1957 Carbon 1.352.25%. Chromium 26-30%. Cobalt 44-51 Tungsten18.75-23.25%. Silicon 1.75% max. Iron 3% max.

The aforesaid alloy may also contain small and inconsequential amountsof residual or trace elements, such as manganese, sulphur and vanadium,and such residual amounts are contemplated as falling within the scopeof the expression the balance being substantially all iron, as used inthe appended claims.

The hardness values, at room temperatures, of alloys Within theaforesaid analysis range, were between 45 Rockwell C and 62 Rockwell C.It was found that increasing the carbon content of the alloy producedhardnesses above 62 Rockwell C, but increased brittleness of the alloy,and that alloys with hardnesses below 45 Rockwell C were notsufficiently resistant to wear or abrasion.

The alloys of the present invention are especially resistant to fatigueat high temperatures, and have been found to be especially useful forapplications for which cobalt-chromium-tungsten alloys of conventionalanalysis ranges have been found to be inadequate.

The alloys may be used either in the form of castings, or as weld rodsfor the hard surfacing of parts which require the properties which areinherent in these alloys.

It may be noted that in contradistinction to known alloys of this type,molybdenum is not substitutable for any part of the tungsten of thealloys of this invention, without materially altering the properties ofthe alloy, anlcal that nickel is not substitutable for any part of theco alt.

It will be understood that slight changes may be made in the alloywithout departing from the scope of the invention, as defined by theappended claims.

Having thus described our invention, we claim:

1. An alloy which is especially resistant to fatigue at hightemperatures, said alloy consisting of carbon in amounts of from about1.35% to about 2.25%, chromium in amounts of from about 26% to about30%, cobalt in amounts of from about 44% to about 51%, tungsten inamounts of from about 18.75% to about 23.25%, and silicon up to amaximum of about 1.75%, the balance of the alloy being substantially alliron, but not to exceed about 3%.

2. An alloy, as defined in claim 1, having a Rockwell C hardness of fromabout 45 to about 62.

References Cited in the file of this patent UNITED STATES PATENTS2,048,706 Pfanstiehl July 28, 1936 2,235,232 McElroy Mar. 18, 19412,299,871 Baird Oct. 27, 1942 2,309,372 Wissler Jan. 26, 1943 2,551,170Schmucker May 1, 1951 2,553,609 Schmidt May 22, 1951

1. AN ALLOT WHICH IS ESPECIALLY RESISTANT TO FATIGUE AT HIGHTEMPERATURES, SAID ALLOY CONSISTING OF CARBON IN AMOUNTS OF FROM ABOUT1.35% TO ABOUT 2.25%, CHROMIUM IN AMOUNTS OF FROM ABOUT 26% TO ABOUT30%, COBALT IN AMOUNTS OF FROM ABOUT 44% TO ABOUT 51%, TUNGSTEN INAMOUNTS OF FROM ABOUT 18.75% TO ABOUT 23.25%, AND SILICON UP TO MAXIMUMOF ABOUT 1.75%, THE BALANCE OF THE ALLOY SUBSTANTIALLY ALL IRON, BUT NOTTO EXCEED ABOUT 3%.